1. Field of the Invention
The present invention relates to a platinum alloy electrocatalyst and an electrode containing the catalyst for use in an acid-electrolyte fuel cell.
2. Description of the Prior Art
Fuel cells are an electrochemical device for directly converting a chemical energy generated from an oxidation-reduction reaction of a fuel such as hydrogen or hydrocarbon and an oxidizer such as oxygen gas supplied thereto, into a low-voltage direct current. They are generally comprised of a fuel electrode(anode), an oxidizer electrode (cathode), an electrolyte interposed between the electrodes, and means for separately supplying a stream of the fuel and a stream of the oxidizer to the anode and the cathode, respectively.
An electrocatalyst is used in the anode and the cathode, and in operation, the fuel supplied to the anode is oxidized on the electrocatalyst in the presence of the electrolyte to release electrons. On the other hand, the oxidizer supplied to the cathode is reduced on the electrocatalyst in the presence of the electrolyte while consuming the electrons supplied from the anode via an external circuit. At this time, the current flowing through the external circuit is utilized as power under a fixed load.
Currently, a phosphoric acid fuel cell is thought to be the nearest to commercial use. However, the electrocatalyst used therein has long had two major problems; that is, the activation polarization of the oxygen reduction reaction at the cathode is far greater than that of the hydrogen oxidation reaction at the anode, and moreover, in the coexistence of the electrolyte at the high temperatures of 190.degree.-210.degree. C. and oxygen as an oxidizer, dissolution and sintering of active metal readily proceed, resulting in deterioration of activity.
In recent years, in order to develop a fuel cell having a high efficiency, a long life and a low cost, studies have been made to develop catalysts comprising an electrically conductive carbon powder carrier and a platinum-base metal multi component alloy deposited thereon, such as supported platinum-chromium-cobalt ternary alloy catalyst (U.S. Pat. Nos. 4,447,506 and 4,711,829), supported platinum-cobalt-nickel ternary alloy catalysts (Japanese Laid-Open Patent Publication No. 8851/1986), supported platinum-iron-cobalt ternary alloy catalyst (Japanese Laid-Open Patent Publication No. 163,746/1987), supported platinum-copper binary alloy catalyst (Japanese Laid-Open Patent Publication No. 269,751/1987) and supported platinum-chromium-gallium ternary alloy catalyst (U.S. Pat. No. 4,880,711).
However, none of these prior art catalysts satisfies both of the high activity and long life required by practical fuel cells, and there still remains room for improvement.